The Spitzer Survey for Stellar Structure in Galaxies (S4G) and its more recently approved extension will lead to a set of 3.6 and 4.5um images for 2829 galaxies, which can be used to study many different aspects of the structure and evolution of local galaxies. We have collected and re-reduced optical images of 1768 of the survey galaxies, aiming to make these available to the community as ready-to-use FITS files to be used in conjunction with the mid-IR images. Our sky-subtraction and mosaicking procedures were optimised for imaging large galaxies. We also produce false-colour images of some of these galaxies to be used for illustrative and public outreach purposes. We collected and re-processed images in five bands from the Sloan Digital Sky Survey for 1657 galaxies.
We present optical observations of a sample of 57 spiral galaxies and describe the procedures followed to reduce the data. We have obtained images in the optical B and I broad bands, as well as in H{alpha}, with moderate spatial resolution and across wide enough fields to image the complete disks of the galaxies. In addition, we observed 55 of our sample galaxies in the R and eight in the V band, and imaged a subset through a dedicated narrow continuum filter for the H{alpha} line. We describe the data reduction procedures we developed in the course of this work to register, combine and photometrically calibrate each set of images for an individual galaxy. We describe in some detail the procedure used to subtract the continuum emission from our H{alpha} images. In companion papers, we describe near-infrared imaging of the galaxy sample, and present analyses of disk scale lengths, and of properties of bars, rings, and HII regions in the sample galaxies. The images described here will be made available for use by other researchers through the CDS.
This catalog reports on an extensive optical and infrared study of the 178 radio sources in the Parkes Selected Regions (S > 100 mJy at 2.7 GHz). CCD observations have resulted in the essential completion (95 percent) of optical identifications and have provided B and R photometry. In addition, K photometry has been completed for four of the six selected regions.
We combine Herschel/SPIRE submillimetre (submm) observations with existing multiwavelength data to investigate the characteristics of low-redshift, optically red galaxies detected in submm bands. We select a sample of galaxies in the redshift range 0.01<=z<=0.2, having >5{sigma} detections in the SPIRE 250{mu}m submm waveband. Sources are then divided into two sub-samples of red and blue galaxies, based on their UV-optical colours. Galaxies in the red sample account for ~4.2 per cent of the total number of sources with stellar masses M*>~10^10^M_{sun}_. Following visual classification of the red galaxies, we find that >~30 per cent of them are early-type galaxies and >~40 per cent are spirals. The colour of the red-spiral galaxies could be the result of their highly inclined orientation and/or a strong contribution of the old stellar population. It is found that irrespective of their morphological types, red and blue sources occupy environments with more or less similar densities (i.e. the {Sigma}_5_ parameter). From the analysis of the spectral energy distributions of galaxies in our samples based on MAGPHYS, we find that galaxies in the red sample (of any morphological type) have dust masses similar to those in the blue sample (i.e. normal spiral/star-forming systems). However, in comparison to the red-spirals and in particular blue systems, red-ellipticals have lower mean dust-to-stellar mass ratios. Besides galaxies in the red-elliptical sample have much lower mean star formation/specific star formation rates in contrast to their counterparts in the blue sample. Our results support a scenario where dust in early-type systems is likely to be of an external origin.
We present an 8-band (u*, g', r', i', z', Y, J, Ks) optical to near-infrared deep photometric catalogue based on the observations made with MegaCam and WIRCam at CFHT, and compute photometric redshifts, zph in the North Ecliptic Pole (NEP) region, where AKARI infrared satellite carried out deep survey at near to mid infrared wavelength. We designed the catalogue to include sources detected in z' band with counterparts in at least one of the other bands, and found 85797 sources in the NEP field. Comparing with galaxy spectroscopic redshifts, photometric redshift dispersion {sigma}({Delta}z/(1+z)) is 0.032 and catastrophic failure rate {Delta}z/(1+z)>0.15 is 5.8% at z<1. Our redshifts are highly accurate with z'<22 at zph<2.5 and for fainter sources with z'<24 at z<1.
We identify optical counterparts, address uncertain identifications and measure previously unknown redshifts of the host galaxies of candidate Gigahertz Peaked Spectrum (GPS) radio sources, and study their stellar populations. Long slit spectroscopy and deep optical imaging in the B, V and R bands, were obtained with the Very Large Telescope.
Using the 1.56m telescope at Shanghai Observatory, China, we present the photometric results of 1ES 1959+650, which cover from 2006 June 11 to 2014 July 31. The maximum variabilities are {Delta}m_V|max_=1.74+/-0.02mag in the V band, {Delta}m_R|max_=0.97+/-0.02mag in the R band, and {Delta}m_I/max_=1.15+/-0.03mag in the I band. During the monitoring period, we obtain intraday variabilities on 2009 September 2 (JD2455077) and 2009 September 3 (JD2455078). On 2009 September 2, the intraday variabilities are {Delta}m_V_=0.36+/-0.08mag within 1.56hr, {Delta}m_R_=0.21+/-0.04mag within 23minutes, and {Delta}m_I_=0.53+/-0.03mag within 45minutes. On 2009 September 3, the intraday variabilities are {Delta}m_V_=0.40+/-0.10mag within 27minutes, {Delta}m_R_=0.48+/-0.04mag within 3.24hr, and {Delta}m_I_=0.68+/-0.06mag within 3.72hr. The two intraday variabilities occur in 24hr, which may occur in the same variable phase. Other results show that (1) no quasi-periodicity is found in the long-term light curve and (2) the correlations between the brightness and the spectrum show obvious anti-correlation, {alpha}=-(0.18+/-0.02)F_V_+(2.33+/-0.12), with the correlation coefficient r=-0.74 and the chance probability p<0.01%.
Optical photometry in 3 Local Group dwarf galaxies
Short Name:
J/ApJ/756/79
Date:
21 Oct 2021
Publisher:
CDS
Description:
We present deep wide-field photometry of three recently discovered faint Milky Way (MW) satellites: Leo V, Pisces II, and Canes Venatici II. Our main goals are to study the structure and star formation history of these dwarfs; we also search for signs of tidal disturbance. The three satellites have similar half-light radii (~60-90pc) but a wide range of ellipticities. Both Leo V and CVn II show hints of stream-like overdensities at large radii. An analysis of the satellite color-magnitude diagrams shows that all three objects are old (>10Gyr) and metal-poor ([Fe/H]~-2), though neither the models nor the data have sufficient precision to assess when the satellites formed with respect to cosmic reionization. The lack of an observed younger stellar population (<~10Gyr) possibly sets them apart from the other satellites at Galactocentric distances >~150kpc. We present a new compilation of structural data for all MW satellite galaxies and use it to compare the properties of classical dwarfs to the ultra-faints. The ellipticity distribution of the two groups is consistent at the ~2{sigma} level. However, the faintest satellites tend to be more aligned toward the Galactic Center, and those satellites with the highest ellipticity (>~0.4) have orientations ({Delta}{theta}_GC_) in the range 20{deg}<~{Delta}{theta}_GC_<~40{deg}. This latter observation is in rough agreement with predictions from simulations of dwarf galaxies that have lost a significant fraction of their dark matter halos and are being tidally stripped.
We present results of a microvariability polarization study in the violently variable quasar 3C 279. We have resolved the polarization curves in the V band for this object down to timescales of minutes. We found two main components in the evolution of the degree of linear polarization, one consisting of a flicker with timescales of several tens of minutes and other component with far more significant variations on timescales of a few days. The linear polarization descended from ~17% down to ~8% in three nights. The polarization angle underwent a sudden change of more that 10 degrees in a few hours, perhaps indicating the injection of a new shock in the jet. The amplitude of the intranight flickering in the degree of polarization is at the level of ~1%. These are probably the best sampled polarization data ever obtained for this object. We also performed IR observations and we provide a follow-up of the evolution of this source at such energies after the main polarization outburst.
A database for the entire Markarian catalog is presented that combines extensive new measurements of their optical parameters with a literature and database search. The measurements were made using images extracted from the STScI Digitized Sky Survey (DSS) of F_pg_(red) and J_pg_(blue) band photographic sky survey plates obtained by the Palomar and UK Schmidt telescopes. We provide accurate coordinates, morphological type, spectral and activity classes, red and blue apparent magnitudes, apparent diameters, axial ratios, and position angles, as well as number counts of neighboring objects in a circle of radius 50kpc. Special attention was paid to the individual descriptions of the galaxies in the original Markarian lists, which clarified many cases of misidentifications of the objects, particularly among interacting systems, larger galaxies with knots of star formation, possible stars, and cases of stars projected on galaxies. The total number of individual Markarian objects in the database is now 1544.